Conformational isomerization of cis-decahydronaphthalene over zeolite catalysts

Abstract

This paper presents our exploratory studies on zeolite-catalyzed conformational isomerization of cis-decahydronaphthalene ( cis-DeHN, or cis-decalin) to trans-DeHN at relatively low temperatures. The catalytic reactions were mainly conducted at 473–573 K for 0.15–8 h under an initial pressure of 0.79 MPa N 2 or H 2 using six catalysts: a hydrogen Y zeolite, a lanthanum ion-exchanged Y zeolite, a hydrogen mordenite, and three noble metal loaded mordenites. Pt-and Pd-loaded mordenites displayed the highest selectivity towards trans-DeHN (nearly 100%), with a trans-DeHN/ cis-DeHN ratio of about 13 under H 2 at 473 K; however, they are less effective under N 2. Pre-reduction of Pt/HM30A could improve its catalytic effectiveness in N 2 atmosphere. These results reveal a molecular H 2-promoted isomerization reaction. HY, LaHY, and HM30A are not as effective as Pt-and Pd-loaded mordenites, and the catalyst with the lowest acidity (HM30A) displayed the lowest activity as well as selectivity to trans-DeHN. The activity for cis-DeHN conversion decreases in the following order: Pt/HM30A ≈ Pd/HM30A ≈ Pt/HM20A > HY > LaHY > HM30A. An overall kinetic model for the catalytic reaction was proposed and empirical equations capable of predicting reaction conversion and product yield were presented. The theoretical equilibrium compositions of trans-DeHN and cis-DeHN at several temperatures were calculated and corroborated well with the experimental results over effective catalysts such as Pt-and Pd-loaded mordenites. In addition, a lower reaction temperature is found to be thermodynamically favorable.